An in-vivo indwelling medical device such as a catheter, a guide wire, a stent, a pacemaker lead, or an injection needle is in direct contact with a human body tissue, blood, and the like over a long period of time so that, not only biocompatibility such as an anti-thrombotic property, but also abrasive resistance, corrosive resistance, and the like are required.
As a method for imparting biocompatibility, corrosive resistance, and the like to a medical device, there is known a method which covers the base material of the medical device with a diamond-like thin film (DLC film) (see, e.g., Patent Document 1). Because the DLC film has a smooth surface which is chemically inactive, it is less reactive to a biological component, and shows excellent biocompatibility. The DLC film is also a hard material and excellent in abrasive resistance.
However, because of its low adhesion to the base material, the DLC film has the problem of delamination from the surface of the medical device. In particular, a stent or the like needs to perform expansion and contraction in a human body so that the shape thereof significantly changes. As a result, a large stress is added also to the DLC film covering the surface so that the DLC film delaminates or a crack occurs therein.
As a method for improving the adhesion between the DLC film and the base material of the medical device, and suppressing the delamination of the DLC film, there are known a method which forms an intermediate layer between the DLC film and the base material (see, e.g., Patent Document 2), and a method which forms a region having a large number of graphite bonds (SP2 bonds) on the side closer to the base material by adjusting conditions for generating a plasma (see, e.g., Patent Document 3).    Patent Document 1: Japanese Laid-Open Patent Publication No. HEI 11-313884    Patent Document 2: Japanese Laid-Open Patent Publication No. 2006-000521    Patent Document 3: Japanese Laid-Open Patent Publication No. 2003-310744